The present invention relates to a primary part of a linear electrical machine, and to a linear electrical machine with a primary part.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Linear electrical machines have a primary part and a secondary part. The primary part and the second part are opposite one another and are separated from one another by an air gap. The primary part is designed for electric current to be passed through it.
It is possible for both the primary part and the secondary part to have active means for production of magnetic fields. In a situation such as this, for example, the primary part has a winding through which current can be passed, and the secondary part has permanent magnets.
In addition, it is also possible for the primary part to have a plurality of active means for production of magnetic fields, and for the secondary part to be free of such means.
For example, German Offenlegungsschrift DE 10 2004 045 992 A1 discloses an electrical machine wherein the primary part has all the magnetic sources of the electrical machine. In this example, the primary part has a winding through which current can be passed and permanent magnets. In contrast, the secondary part is only a toothed iron reaction rail.
In contrast to electrical machines which operate by rotation, linear electrical machines have end areas, of course, in which the electromagnetic part of the machine ends. If, for example, a linear motor is designed using a short stator construction, that is to say the primary part is a shorter component than a longer secondary part, this results in the primary part having two end areas which are located in the influence area of the secondary part. The ends of the primary part interact with the secondary part such that it has a significant influence on the active force ripple and the passive force ripple, also referred to as the cogging force.
Parasitic cogging forces that occur as a result of the magnetic interaction between the primary part and the secondary part are referred to as passive force ripple. This results in vibration, rough running and drag errors during machining processes.
Furthermore, the induced voltages, i.e., the electromotive force (EMF), in the initial and end coils at the end faces of the primary part are generally less pronounced than in the central coils, owing to the lack of a magnetic return path. In consequence, the electrical machine does not have a symmetrical induced voltage. This results in an additional current-dependent force ripple that is referred to as active force ripple, in addition to reductions in the force.
In accordance with the present invention, a primary part that has a plurality of active means for producing magnetic fields is provided for use in a linear electrical machine that reduces active and passive force ripple, i.e., cogging force, in the linear electrical machine.
It would be desirable and advantageous to address prior art shortcomings and to attain reduced active and passive force ripple, i.e. cogging force.